Diffusion bonding is dependent upon clamping pressure, temperature, time, surface finish, material properties, and amount of surface contamination and oxidation. Hence, it is art at best. Variations in the thickness of the metals being diffusion bonded can result in unwanted non-bonded areas.
Compact high intensity coolers or heat exchangers (CHIC) are known. Unlike conventional heat exchangers, the former can efficiently handle relatively high heat fluxes in a small volume with relatively low power requirements for pumping a heat exchange fluid, see for example U.S. Pat. No. 4,559,580. These heat exchangers comprise a series of plates or laminates including alternating orifice plates and baffle plates. The orifice plates have coolant flow impingement orifices extending therethrough. U.S. Pat. No. 4,494,171 discloses another example of an impingement cooling apparatus for heat liberating device.
A CHIC heat exchanger may have layers, e.g. its lamination or plates, as thin as 0.004 inch thick. A small local deviation in the thickness of these layers may be enough to cause a leak because the diffusion bonded connections between the respective layers are not continuous. It is nearly impossible to detect internal areas of non-bonding in these heat exchangers. Nevertheless, external leakage is not acceptable. Moreover, in two fluid systems, internal leakage of for example fuel and ethylene glycol, cannot be tolerated. Thus, there is a need for an improved method of diffusion bonding which can be employed in making heat exchangers such as CHIC heat exchangers for preventing both external and internal leakage of fluid circulated in the heat exchanger by ensuring continuous diffusion bonds in critical areas.
U.S. Pat. No. 3,441,996 discloses a method of manufacturing laminated fluid amplifiers wherein the laminations of the fluid amplifier can be diffusion bonded. U.S. Pat. No. 4,566,625 discloses a method for diffusion welding particularly applicable for welding pipe sections of a pipeline for offshore transportation of gas and oil wherein the joint is configured so that a high surface pressure occurs along the periphery of the joint at the beginning of the method.